Question

cosx1-sosx2=-2sin(x1+x2)/2*sin(x2-x1)/2如何计算的?

Answer 1

cosx1=cos((x1+x2)/2 - (x2-x1)/2);
cosx2=cos((x1+x2)/2 + (x2-x1)/2);
cos(a+b)=cosacosb-sinasinb;
cos(a-b)=cosacosb+sinasinb;